CartesianProductIterator

var a = new Arrays.asList('a1', 'a2', 'a3');
var b = new Arrays.asList('b1', 'b2', 'b3');
var c = new Arrays.asList('c1', 'c2', 'c3');
var d = new Arrays.asList('d1', 'd2', 'd3');
var e = new Arrays.asList('e1', 'e2', 'e3');
var f = new Arrays.asList('f1', 'f2', 'f3');

for (var aElement : a) {
    for (var bElement : b) {
        for (var cElement : c) {
            for (var dElement : d) {
                for (var eElement : e) {
                    for (var fElement : f) {
                        // ...
                    }
                }
            }
        }
    }
}

var it = new CartesianProductIterator<>(a, b, c, d, e, f);
while (it.hasNext()) {
    var elements = it.next();
}